Safety First with Friction-Element Action Triggered by Spring Engagement

MOTION SYSTEM APPLICATIONS

Safety first with friction-element action triggered by spring engagement

FRICTION-BASED brakes and clutches that use springs (typically axial- compression coil springs) for engagement are an exceptionally important class of components. No wonder their variations often justify unique designations that ﬁ machine designs. These include certain:

• Spring-set brakes • Failsafe brakes • Slip clutches • Safety and e-stop brakes • Holding brakes • Servomotor brakes

The power-off designation emphasizes how these particular components default to a spring-loaded condition that brings attached loads to a nonmoving state upon removal of release power. That means the mode of disengagement for these units is quite important as well. In most cases, these brakes and clutches are released in one of two ways:

• They are electromagnetically released • They are pneumatically released

The electrification of off-road vehicles During electromagnetic disengagement, propelled by motor-based direct drives ﬁ (spurred by the advancement of longer- counteracts the spring force clamping together the life battery technologies) has prompted friction elements and separates friction elements. innovation in brake and clutch During pneumatic disengagement, application of power technology as well. RANGER Pursuit EV occurs via air pressure in a piston chamber — which in vehicle image courtesy Polaris turn counteracts the spring force clamping together the friction elements and releases the friction-based hold … for independent rotation of the axis output.

12 DESIGN WORLD — MOTION 11 • 2020 motioncontroltips.com | designworldonline.com BRAKES & CLUTCHES

SPRING-SET ELECTROMAGNETICALLY RELEASED FRICTION-DISC CLUTCH BRAKE

In power-off friction brakes, spring pressure forces the friction discs (or ARMATURE COIL SPRING elements) into engagement to stop and ARRAY hold the load. Then an electromagnetic or pneumatic release system spreads the elements apart to disengaging the unit. Such spring engagement offer a key advantage — the ability to serve as failsafe brakes even during power loss. That contrasts with the electromagnetically engaged brakes.

FLOATING HUB FRICTION PLATES ATTACHES TO MOTOR ON ROTOR

Spring-set hub-style brakes mount on the ends of electric motors. In contrast, coupling-type brakes install between the motor and driven load.

Where the hub-style brake operates on a precision motion axis (and the braking function affectsperformance) a mode of attachment having minimal Spring backlash is paramount. Applied SPLINE IS ESPECIALLY SECURE Brakes

Clutches based on spring force and friction-plate action are often used to transmit mechanical power from a constantly rotating motor-output shaft to some end-of-axis process requiring only intermittent rotation. From the world’s largest manufacturer of One of two common variations (in which a clutch hub world-class electromagnetic clutches and brakes assembly directly attaches to the motor drive shaft and not the output) includes: Electromagnetic clutches & brakes for virtually every application ﬁ For holding and stopping applications (to apply lateral force for disengagement) either a pneumatic inlet A wide array of standard torque and internal circuit (as well as an exhaust port for quick response) or ranges (1.75in/lbs - 880 in/lbs) wiring and a coil for electromagnetic action Custom designed and manufactured for your • A moving (rotating) axis-output sleeve assembly containing application friction discs and upon which an output pulley, pinion gear, or Manual release, zero backlash, and adjustable sheave bolts torque also available • A drive hub enclosed by the housing and sleeve — and having SEE HOW IT WORKS! ﬁ Inch and metric bores available elements) as well as an armature if a typical electromagnetically 100 Randolph Road • Somerset, NJ 08873 released unit Phone: 732-271-7361 • Fax: 732-271-7580 https://ogura-clutch.com/spring • [email protected]

11 • 2020 DESIGN WORLD — MOTION 13 MOTION SYSTEM APPLICATIONS

Without any external power, the housing assembly’s springs push together the sleeve’s friction discs and the hub’s ﬁ ns. Then for disengagement, either electromagnetic or pneumatic-cylinder force compresses the springs to allow the ﬁ ns and friction discs to disengage.

Brakes based on spring force for friction- plate action are by default locked, because in the absence of any external power, mechanical springs hold stationary-side plates, ﬁ ns, or friction discs in engaged contact with drive-side friction discs. No wonder the failsafe function of many of these brakes is indispensable in medical diagnostic equipment as well as general automation relayed to discrete motion control and servomotor “ designs such as robotics and mobile How thin do you need to be? equipment complemented by holding brakes.

(RNB-T and MCNB-T) Innovations in new and advancing applications are spurring a widening Ogura electromagnetic thin style holding brakes: Ultra-thin style of array of brake uses — as well as holding brakes are designed to reduce the overall footprint of a motor increased safety for end users. brake package. Through internal ux improvements, brakes are thin- That’s especially true of spring-set ner and lighter but can produce similar torques of previous designs. electrically released brakes.

Standard brakes are rated up to 50 Nm / 37 lb-ft. Custom designs with These have undergone signi cant thermistors and built-in sensors are possible. Brakes are primarily innovation over the past several designed for holding but can accommodate emergency stops. Some years as developments in friction coils are designed for low power operation (12V) but 24V is required materials and spring designs for brake disengagement. Brakes are primarily used for robotics, warehouse automation, medical equipment, electric vehicle parking have enabled use in myriad new brakes and on various stepper and servomotors. applications — especially in medical and personal-mobility industries. Benets you will see using Ogura holding brakes: Torque is electrically controlled over a very wide speed range Strengths: Spring-set brakes are a top Units are sealed and do not produce wear particles choice for emergency-braking applications on Larger units are available with fans for forced air cooling, providing additional heat dissipation the motor-driven axes of robotic arms, vertical Extremely fast torque response axes, and machines that have the capacity to Units can be sized for continuous slip injure personnel should a power failure occur. That includes escalators, airport-baggage handlers, and elevators. They also beneﬁ t motion designs that slow loads with the

14 DESIGN WORLD — MOTION BRAKES & CLUTCHES

motor before the brake engages … and they’re suitable as Constraints: The force applied by the springs in holding mechanisms as well. spring-set units is a factor that limits the maximum torque There are also countless variants of spring-set brakes rating. In addition, the maximum force of the disengaging fi system in a spring-set unit must be well matched to the servo applications. Many of these have low-backlash hub spring force to be overcome during power-on release coupling morphology. That means they have a female situations. More basic spring-set brakes and clutches can spline subcomponent on their friction-element assembly also introduce excessive impulse and shock loading on that precisely mates with a matching square, D-shaped, precision operations. polygon, or hexagon-shaped spline on the electric motor Case in point: Consider an inclined conveyor with output shaft (or in some cases the driven shaft). regularly spaced on-off cycles. Here, a power-off brake that Precision-machined splines help minimize (and fi fi power failures. But advanced conveyor installations working associated with the internal clearances needed to let the to position discrete product of varied size (without jerking) friction elements run free (unengaged) upon application may need multiple deceleration rates via more sophisticated of pneumatic or electromagnetic power. Some units spring-set or other brakes complemented by an advanced even incorporate diaphragm springs for zero-backlash motor-and-drive pairing. operation. Otherwise, typical no-load backlash (depending on the component diameter) might be 0.2° to 0.8° or so.

motioncontroltips.com | designworldonline.com 11 • 2020 DESIGN WORLD — MOTION 15